Disclosed are examples of techniques for enabling communication between synchronous and asynchronous processes. More specifically, interaction between synchronous and asynchronous web services in a network environment is enabled.
The web service provider market is one of the fastest growing segments of the software industry. Web service providers make enterprise applications, such as human resources administration, recruiting, travel and expense management, sales force automation, and so on, available to customers over the web on a subscription basis, or for free. These enterprise applications are fully managed and hosted by the web service providers, which results in significant cost savings for enterprises using the web services and eliminates many of the issues requiring individual enterprise application integration (EAI) solutions.
Some web service providers merely host and manage third-party packaged software for their customers (i.e., “managed hosters”). Others build new applications from the ground up to take advantage of the benefits and cost-savings of the web service provider model. Web service providers enjoy the profit margins and operational scalability of consumer Web companies like eBay and Yahoo, while at the same time offering the feature sets of complex enterprise software applications such as PeopleSoft and Siebel.
Client applications can locate the web services using a UDDI (Universal Description, Discovery, and Integration) service, which is based on XML (eXtended Markup Language) and SOAP (Single Object Access Protocol). XML is a markup language for documents containing structured information, that is, the information and an indication of its role, and is a common way to provide information over wide area networks, such as the Internet. SOAP is an XML-based protocol for exchanging information in a decentralized, distributed environment. SOAP can be used in combination with a variety of protocols, but its most frequent use is in conjunction with HTTP (Hyper Text Transfer Protocol). Web service providers can register contact addresses and descriptions of the provided web services in a UDDI directory, and prospective clients can use the UDDI directory as a “phone book for web services,” and look up web services that fit the clients' needs.
Web services are typically described in a Web Service Description Language (WSDL), which is an XML-based format. WSDL enables separation of the description of the abstract functionality offered by a web service from concrete details of a service description, such as “where” and “how” the functionality is offered. WSDL describes web services starting with the messages that are exchanged between the web service provider and a requestor. The messages are first described abstractly and are then bound to a concrete network protocol and message format. A message consists of a collection of typed data items. A message exchange between the web service provider and the requestor is referred to as an operation. A collection of operations is a portType. Collections of portTypes are grouped and referred to as a service. A web service represents an implementation of a service and contains a collection of ports, where each port is an implementation of a portType, which includes all the concrete details the requestor needs in order to interact with the web service.
Two main communication models exist for communication between a requestor and a web service: a synchronous communication model and an asynchronous communication model. In the synchronous communication model, a requestor communicates synchronously with a synchronous web service, that is, the requestor sends a request to the web service and waits until a response is returned. The requestor is prevented from performing any other operations until the response is received.
In the asynchronous communication model, on the other hand, a requestor communicates asynchronously with a web service, that is, the requestor sends a request to the web service, some time may pass, and a response is returned by the web service. The requestor may perform other operations while waiting for the response from the web service. Currently, the two communication models cannot work in conjunction, and as a consequence there is no way for a synchronous requestor to communicate directly with an asynchronous web service, or for an asynchronous requestor to communicate directly with a synchronous web service.